® RT8296B 3A, 23V, 1.2MHz Synchronous Step-Down Converter General Description Features The RT8296B is a high-efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 3A output current from a 4.5V to 23V input supply. The RT8296B's current mode architecture and external compensation allow the transient response to be optimized over a wide range of loads and output capacitors. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. Fault conditions also include output under voltage protection and thermal shutdown protection. The low current (<3μA) shutdown mode provides output disconnection, enabling easy power management in battery-powered systems. The RT8296B is available in an SOP-8 (Exposed Pad) package. Ordering Information RT8296B Package Type SP : SOP-8 (Exposed Pad-Option 1) Lead Plating System G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free) H : UVP Hiccup L : UVP Latch-Off Note : Richtek products are : 4.5V to 23V Input Voltage Range 3A Output Current Integrated N-MOSFET Switches Current Mode Control Fixed Frequency Operation : 1.2MHz Adjustable Output from 0.8V to 15V Up to 95% Efficiency Programmable Soft-Start Stable with Low-ESR Ceramic Output Capacitors Cycle-by-Cycle Over Current Protection Input Under Voltage Lockout Output Under Voltage Protection Thermal Shutdown Protection RoHS Compliant and Halogen Free Applications External Storage Device Wireless AP/Router Set-Top-Box Industrial and Commercial Low Power Systems LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation of High-Performance DSPs Pin Configurations (TOP VIEW) RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ±1.5% High Accuracy Feedback Voltage Suitable for use in SnPb or Pb-free soldering processes. Marking Information BOOT VIN 2 SW GND 3 GND 8 SS 7 EN 6 COMP 5 FB 9 4 RT8296BxGSP RT8296BxGSP : Product Number RT8296Bx GSPYMDNN SOP-8 (Exposed Pad) x : H or L YMDNN : Date Code RT8296BxZSP RT8296BxZSP : Product Number RT8296Bx ZSPYMDNN x : H or L YMDNN : Date Code Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8296B Typical Application Circuit 2 VIN 4.5V to 23V CIN 10µF x 2 REN 100k CSS 0.1µF BOOT VIN 1 RT8296B SW 3 7 EN 8 SS 4, 9 (Exposed Pad) GND CBOOT L 100nF 3.6µH R1 75k FB 5 COMP 6 CC 2.2nF RC 22k VOUT 3.3V/3A COUT 22µF x 2 R2 24k CP Open Table 1. Recommended Component Selection VOUT (V) R1 (k) R2 (k) RC (k) CC (nF) L (H) COUT (F) 8 27 3 51 2.2 10 22 x 2 5 62 11.8 33 2.2 6.8 22 x 2 3.3 75 24 22 2.2 3.6 22 x 2 2.5 25.5 12 16 2.2 3.6 22 x 2 1.5 10.5 12 10 2.2 2 22 x 2 1.2 12 24 8.2 2.2 2 22 x 2 1 3 12 6.8 2.2 2 22 x 2 Functional Pin Description Pin No. Pin Name Pin Function Bootstrap for High Side Gate Driver. Connect a 0.1F or greater ceramic capacitor from BOOT to SW pins. Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large ceramic capacitor. 1 BOOT 2 VIN 3 SW Switch Node. Connect this pin to an external L-C filter. GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 5 FB Feedback Input. This pin is connected to the converter output. It is used to set the output of the converter to regulate to the desired value via an internal resistive voltage divider. For an adjustable output, an external resistive voltage divider is connected to this pin. 6 COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. 7 EN Chip Enable (Active High). A logic-low forces the RT8296B into shutdown mode reducing the supply current to less than 3A. Attach this pin to VIN with a 100k pull up resistor for automatic startup. 8 SS Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1F capacitor sets the soft-start period to 13.5ms. 4, 9 (Exposed Pad) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Function Block Diagram VIN Internal Regulator Oscillator Slope Comp Shutdown Comparator VA VCC 1.2V Foldback Control + - 5k EN 0.4V Lockout Comparator 2.7V 3V Current Sense Amplifier + VA - + BOOT UV Comparator + VCC S + R Current Comparator Q 85m Q 85m SW GND 6µA 0.8V SS + +EA - FB Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 COMP is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8296B Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------ −0.3V to 25V Switch Node Voltage, VSW ---------------------------------------------------------------------------------------- −0.3V to (VIN + 0.3V) Switch Node Voltage, VSW, < 10ns ----------------------------------------------------------------------------- −5V to 25.3V BOOT Pin Voltage, VBOOT ---------------------------------------------------------------------------------------- −0.3V to 31.3V VBOOT - VSW ----------------------------------------------------------------------------------------------------------- −0.3V to 6V Other Pin Input Voltages ------------------------------------------------------------------------------------------ −0.3V to 6V Power Dissipation, PD @ TA = 25°C SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------SOP-8 (Εxposed Pad), θJC -------------------------------------------------------------------------------------- Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------ Junction Temperature ---------------------------------------------------------------------------------------------- Storage Temperature Range ------------------------------------------------------------------------------------- ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------- Recommended Operating Conditions 1.333W 75°C/W 15°C/W 260°C 150°C −65°C to 150°C 2kV (Note 4) Supply Voltage, VIN ------------------------------------------------------------------------------------------------- 4.5V to 23V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Shutdown Supply Current VEN = 0V -- 0.5 3 A Supply Current VEN = 3V, VFB = 0.9V -- 0.8 1.2 mA 0.788 0.8 0.812 V -- 940 -- A/V RDS(ON)1 -- 85 -- m RDS(ON)2 -- 85 -- m -- 0 10 A 3.6 5.1 6.6 A GCS -- 5.4 -- A/V fOSC1 1 1.2 1.4 MHz -- 270 -- kHz Feedback Voltage Error Amplifier Transconductance High Side Switch On-Resistance Low Side Switch On-Resistance High Side Switch Leakage Current Upper Switch Current Limit COMP to Current Sense Transconductance Oscillation Frequency Short Circuit Oscillation Frequency VFB 4.5V VIN 23V GEA IC = ±10A VEN = 0V, VSW = 0V Min. Duty Cycle, VBOOTVSW = 4.8V fOSC2 VFB = 0V Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Parameter Symbol Test Conditions Typ Max Unit -- 75 -- % ns Maximum Duty Cycle DMAX Minimum On-Time t ON -- 100 -- Logic-High VIH 2.7 -- 5.5 Logic-Low Input Under Voltage Lockout Threshold Input Under Voltage Lockout Hysteresis Soft-Start Current VIL -- -- 0.4 3.8 4.2 4.5 V -- 320 -- mV I SS VSS = 0V -- 6 -- A Soft-Start Period t SS CSS = 0.1F -- 13.5 -- ms Thermal Shutdown T SD -- 150 -- C EN Input Voltage VUVLO VFB = 0.7V Min VIN Rising VUVLO V Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8296B Typical Operating Characteristics Reference Voltage vs. Input Voltage Efficiency vs. Output Current 0.820 90 0.815 Reference Voltage (V) 100 Efficiency (%) 80 70 VIN = 12V VIN = 23V 60 50 40 30 0.810 0.805 0.800 0.795 0.790 20 0.785 10 VOUT = 3.3V 0 0.01 0.780 0.1 1 10 4 6 8 10 Output Current (A) 0.815 3.35 0.810 0.805 0.800 0.795 0.790 24 VIN = 23V 3.30 3.27 75 100 VIN = 12V VOUT = 3.3V 0 125 0.5 1 1.5 2 2.5 3 Output Current (A) Temperature (°C) Frequency vs. Temperature Frequency vs. Input Voltage 2.00 2.0 1.80 1.8 1.60 1.6 Frequency (MHz)1 Frequency (MHz)1 22 3.31 0.780 50 20 3.32 3.28 25 18 3.33 3.29 0 16 3.34 0.785 -25 14 Output Voltage vs. Output Current 3.36 Output Voltage (V) Reference Voltage (V) Reference Voltage vs. Temperature 0.820 -50 12 Input Voltage (V) 1.40 1.20 1.00 0.80 0.60 1.4 1.2 1.0 0.8 0.6 0.4 0.40 0.20 0.2 VOUT = 3.3V, IOUT = 0.5A VOUT = 3.3V, VIN = 12V, IOUT = 0.5A 0.0 0.00 4 6 8 10 12 14 16 18 20 22 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 24 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Output Current Limit vs. Input Voltage Current Limit vs. Temperature 8.0 6.0 5.5 Output Current Limit (A) Current Limit (A) 7.5 7.0 6.5 6.0 5.5 5.0 4.5 VIN = 12V, VOUT = 3.3V 4.0 5.0 4.5 VOUT = 1.2V VOUT = 3.3V (Add Bootstrap Diode) VOUT = 3.3V 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 VIN = 12V 0.0 -50 -25 0 25 50 75 100 125 4 6 8 10 12 14 16 18 20 Temprature (°C) Input Voltage (V) Load Transient Response Load Transient Response VOUT (50mV/Div) VOUT (50mV/Div) IOUT (1A/Div) IOUT (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0.3A to 3A Time (100μs/Div) Switching Switching VOUT (5mV/Div) VSW (10V/Div) VSW (10V/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A Time (0.5μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 24 VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A Time (100μs/Div) VOUT (5mV/Div) 22 IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (0.5μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8296B Power Off from VIN Power On from VIN VIN (5V/Div) VOUT (2V/Div) VIN (5V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (10ms/Div) Time (10ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Application Information 5V The RT8296B is a synchronous high voltage buck converter that can support an input voltage range from 4.5V to 23V and the output current can be up to 3A. BOOT 100nF RT8296B Output Voltage Setting SW The resistive voltage divider allows the FB pin to sense the output voltage as shown in Figure 1. Figure 2. External Bootstrap Diode VOUT Soft-Start R1 The RT8296B contains an external soft-start clamp that gradually raises the output voltage. The soft-start timing can be programmed by the external capacitor between SS pin and GND. The chip provides a 6μA charge current for the external capacitor. If 0.1μF capacitor is used to set the soft-start, the period will be 13.5ms(typ.). FB RT8296B R2 GND Figure 1. Output Voltage Setting The output voltage is set by an external resistive voltage divider according to the following equation : VOUT Chip Enable Operation = VFB 1 R1 R2 The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT8296B quiescent current will drop below 3μA. Driving the EN pin high (>2.7V, < 5.5V) will turn on the device again. For external timing control (e.g.RC), the EN pin can also be externally pulled high by adding a REN* resistor and C EN * capacitor from the VIN pin (see Figure 5). where VFB is the feedback reference voltage (0.8V typ.). External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate driver voltage for the high side MOSFET. It is recommended to add an external bootstrap diode between an external 5V and BOOT pin for efficiency improvement when input voltage is lower than 5.5V or duty cycle is higher than 65% .The bootstrap diode can be a low cost one such as IN4148 or BAT54. The external 5V can be a 5V fixed input from system or a 5V output of the RT8296B. Note that the external boot voltage must be lower than 5.5V. 2 VIN REN 100k BOOT VIN CIN 1 CBOOT RT8296B 7 EN Chip Enable An external MOSFET can be added to implement digital control on the EN pin when no system voltage above 2.5V is available, as shown in Figure 3. In this case, a 100 kΩ pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. SW 3 VOUT Q1 CSS L R1 8 SS 4, 9 (Exposed Pad) GND COUT FB 5 COMP 6 CC RC R2 CP Figure 3. Enable Control Circuit for Logic Control with Low Voltage Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8296B To prevent enabling circuit when VIN is smaller than the VOUT target value, a resistive voltage divider can be placed between the input voltage and ground and connected to the EN pin to adjust IC lockout threshold, as shown in VIN 12V 2 REN1 100k CIN 10µF BOOT VIN Figure 4. For example, if an 8V output voltage is regulated from a 12V input voltage, the resistor, REN2, can be selected to set input lockout threshold larger than 8V. 1 CBOOT RT8296B 7 EN SW 3 REN2 CSS L VOUT 8V R1 8 SS 4, 9 (Exposed Pad) GND COUT FB 5 COMP 6 CC RC R2 CP Figure 4. The Resistors can be Selected to Set IC Lockout Threshold Hiccup Mode For the RT8296BH, it provides Hiccup Mode Under Voltage Protection (UVP) is provided. When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered and the RT8296BH will shut down for a period of time and then recover automatically. The Hiccup Mode UVP can reduce input current in short-circuit conditions. Latch-Off Mode For the RT8296BL, it provides Latch-Off Mode Under Voltage Protection (UVP) is provided. When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP will be triggered and the RT8296BL will shut down in Latch-Off Mode. In shutdown condition, the RT8296BL can be reset via the EN pin or power input VIN. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. V V IL = OUT 1 OUT VIN f L Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve this goal. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 For the ripple current selection, the value of ΔIL = 0.24(IMAX) will be a reasonable starting point. The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation : VOUT VOUT L = 1 VIN(MAX) f I L(MAX) The inductor's current rating (caused a 40°C temperature rising from 25°C ambient) should be greater than the maximum load current and its saturation current should be greater than the short circuit peak current limit. Please see Table 2 for the inductor selection reference. Table 2. Suggested Inductors for Typical Application Circuit Component Supplier Series Dimensions (mm) TDK VLF10045 10 x 9.7 x 4.5 TDK TAIYO YUDEN SLF12565 12.5 x 12.5 x 6.5 NR8040 8x8x4 CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B V IRMS = IOUT(MAX) OUT VIN VIN 1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = I OUT /2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. For the input capacitor, two 10μF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to Table 3 for more detail. The selection of COUT is determined by the required ESR to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔVOUT , is determined by : 1 VOUT IL ESR 8fCOUT The output ripple will be highest at the maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirement. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors have the highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD (ESR) and COUT also begins to be charged or discharged to generate a feedback error signal for the regulator to return VOUT to its steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. EMI Consideration Since parasitic inductance and capacitance effects in PCB circuitry would cause a spike voltage on the SW pin when high side MOSFET is turned-on/off, this spike voltage on SW may impact on EMI performance in the system. In order to enhance EMI performance, there are two methods to suppress the spike voltage. One way is by placing an R-C snubber between SW and GND and locating them as close as possible to the SW pin (see Figure 5). Another method is by adding a resistor in series with the bootstrap capacitor, CBOOT, but this method will decrease the driving capability to the high side MOSFET. It is strongly recommended to reserve the R-C snubber during PCB layout for EMI improvement. Moreover, reducing the SW trace area and keeping the main power in a small loop will be helpful on EMI performance. For detailed PCB layout guide, please refer to the section Layout Considerations. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8296B 2 VIN 4.5V to 23V REN* Chip Enable CIN 10µF x 2 BOOT VIN 1 RBOOT* CBOOT L 100nF 3.6µH RT8296B SW 3 7 EN RS* CEN* GND R1 75k CS* 8 SS CSS 4, 0.1µF 9 (Exposed Pad) VOUT 3.3V/3A COUT 22µFx2 FB 5 COMP CC 2.2nF 6 RC 22k R2 24k CP NC * : Optional Figure 5. Reference Circuit with Snubber and Enable Timing Control Thermal Considerations design. The thermal resistance θJA can be decreased by For continuous operation, do not exceed the maximum operation junction temperature 125°C. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : adding copper area under the exposed pad of SOP-8 (Exposed Pad) package. Where T J(MAX) is the maximum operation junction temperature , TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification, the maximum junction temperature is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For SOP-8 (Exposed Pad) package, the thermal resistance θJA is 75°C/W on the standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W (min.copper area PCB layout) P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W (70mm2copper area PCB layout) The thermal resistance θJA of SOP-8 (Exposed Pad) is determined by the package architecture design and the PCB layout design. However, the package architecture design had been designed. If possible, it's useful to increase thermal performance by the PCB layout copper Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. The derating curves in Figure 7 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. 2.2 Four-Layer PCB 2.0 Power Dissipation (W) PD(MAX) = (TJ(MAX) − TA ) / θJA As shown in Figure 6, the amount of copper area to which the SOP-8 (Exposed Pad) is mounted affects thermal performance. When mounted to the standard SOP-8 (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W. Adding copper area of pad under the SOP-8 (Exposed Pad) (Figure 6.b) reduces the θJA to 64°C/W. Even further, increasing the copper area of pad to 70mm2 (Figure 6.e) reduces the θJA to 49°C/W. 1.8 1.6 Copper Area 70mm2 50mm2 30mm2 10mm2 Min.Layout 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 7. Derating Curve of Maximum Power Dissipation is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Layout Consideration For best performance of the RT8296B, the following layout guidelines must be strictly followed. (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W Input capacitor must be placed as close to the IC as possible. SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. The feedback components must be connected as close to the device as possible (b) Copper Area = 10mm2, θJA = 64°C/W (c) Copper Area = 30mm2 , θJA = 54°C/W (d) Copper Area = 50mm2 , θJA = 51°C/W (e) Copper Area = 70mm2 , θJA = 49°C/W Figure 6. Themal Resistance vs. Copper Area Layout Design Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8296B-05 July 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8296B VIN GND SW GND The feedback components must be connected as close to the device as possible. CC CIN CSS Input capacitor must be placed as close to the IC as possible. BOOT RS* CS* VIN 2 SW 3 GND 4 GND 8 SS 7 EN 6 COMP 5 FB 9 COUT CP SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. RC R1 R2 L VOUT REN VIN VOUT GND Figure 8. PCB Layout Guide Table 3. Suggested Capacitors for CIN and COUT Location Component Supplier Part No. Capacitance (F) Case Size CIN MURATA GRM31CR61E106K 10 1206 CIN TDK C3225X5R1E106K 10 1206 CIN TAIYO YUDEN TMK316BJ106ML 10 1206 COUT MURATA GRM31CR60J476M 47 1206 COUT TDK C3225X5R0J476M 47 1210 COUT MURATA GRM32ER71C226M 22 1210 COUT TDK C3225X5R1C22M 22 1210 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8296B-05 July 2014 RT8296B Outline Dimension H A M EXPOSED THERMAL PAD (Bottom of Package) Y J X B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.000 0.152 0.000 0.006 J 5.791 6.200 0.228 0.244 M 0.406 1.270 0.016 0.050 X 2.000 2.300 0.079 0.091 Y 2.000 2.300 0.079 0.091 X 2.100 2.500 0.083 0.098 Y 3.000 3.500 0.118 0.138 Option 1 Option 2 8-Lead SOP (Exposed Pad) Plastic Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8296B-05 July 2014 www.richtek.com 15